With development of technology of high-level servers, the transmission speed and quality of signals transmitted by a signal transmission board, e.g., a printed circuit board (PCB), are highly demanded.
A circuit board includes a transmission wire and a plated through hole (PTH). The transmission wire is used for signal transmission in a horizontal direction. The PTH is used for signal transmission in a vertical direction such that the signal can be transmitted through several stacked layers. However, the PTH in vertical direction has impedance mismatch with the transmission wire in horizontal direction, which reduces the speed and quality of the signal transmission. Specifically, when the PTH has impedance mismatch with the transmission wire and a signal is transmitted through several layers in the transmission wire and the PTH, the signal may be undesirably reflected due to the differences between the impedances of the PTH and the transmission wire. Thus, this causes loss and noise of the signal transmission.